PREPARATION OF ENVIRONMENTAL FRIENDLY · PDF filedispersing, emulsifying, stabilizing, foaming, conditioning and anti-foaming agents in many ... detergents, soaps, ... acid neutralizing

Proceedings of the 6th International Conference on Mechanics and Materials in Design,

Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015

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PAPER REF: 5449

PREPARATION OF ENVIRONMENTAL FRIENDLY BENZENE-FREE

METAL SULFONATE SURFACTANT FOR LUBRICANT ADDITIVE

FORMULATION

EunMin Song1, DoWon Kim

1, ByungJo Kim

2, JongChoo Lim

1(*)

1Department of Chemical and Biochemical Engineering, Dongguk University-Seoul, Korea

2AK ChemTech Central Research Lab., DaeJeon, Korea

(*)Email: [email protected]

ABSTRACT

In this study, environmental friendly benzene-free metal sulfonate surfactants were

synthesized for lubricant formulation and the structure of intermediates and final products

were elucidated by 1H NMR,

13C-NMR and FT-IR. Also, the interfacial properties including

critical micelle concentration (CMC), surface tension, contact angle, interfacial tension, foam

stability and emulsion stability were measured. The biodegradability and long-term stability

of the resulting products were characterized and the performances of prepared lubricants were

measured such as oil stain protection, rust inhibition and lubrication and compared with that

of lubricant based on LAS (linear alkyl benzene sulfonate).

Keywords: Benzene-free metal sulfonate surfactant, Lubricant additive, Interfacial property,

Lubrication property

INTRODUCTION

Colloidal additives have been widely used as detergents for many years in lubricant

formulations to prevent the formation of varnish lacquer in the combustion engine and to

neutralize acidic products formed during combustion, which can be the source of corrosion

and lubricant degradation. In addition, the detergents are also known to play an important role

as antiwear, extreme pressure and antioxidant additives. Colloidal lubricant additives mainly

consist of high molecular-weight surfactant, colloidal particles of metal carbonate, and diluent

oil. In the composition of lubricant detergents, colloidal particles of metal carbonate provide

the required total base number (TBN) as a neutralizing agent, while the diluent oil acts as a

compatible agent and surfactants provide steric stabilization around the colloidal particles in a

non-polar oil medium.

Surfactants have been known to play a very important role as cleaning, solubilizing, wetting,

dispersing, emulsifying, stabilizing, foaming, conditioning and anti-foaming agents in many

practical industrial applications. For example, surfactants have a wide variety of applications

ranging from being the active ingredients in household cleaning formulations such as laundry

detergents, soaps, and shampoos to industrial use in petroleum production and textile

processing. Various surfactants such as calcium (or magnesium or barium) sulfonate (or

phenate, salicylate, or phosphonate) have been used to stabilize the colloidal particles of metal

carbonate in the lubricants. Among them, anionic surfactants such as LAS (linear alkyl

benzene sulfonate) and DBSA (dodecyl benzene sulfonic acid) have been widely used in the

formulation of lubricants since the surfaces of metal carbonate particles are predominantly

positively charged. Thus, the adsorption of anionic surfactant molecules on the surface of

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Tribology, Gears and Transmissions

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metal carbonate particles with a head-on configuration decreases the hydrophilicity of

particles since the external surfaces are covered by the hydrophobic chains of the adsorbed

surfactant molecules. As a result, surface activity at the metal carbonate particles is promoted

by in situ surface activation by their interaction with negatively charged anionic surfactant

molecules and the colloidal particle can be stabilized in a non-polar oil medium.

As mentioned above, anionic surfactants such as LAS and DBSA have been widely as

detergent, dispersant, anti-oxidant and corrosion inhibitor mainly due to excellent

performance and relatively low cost. However, these products based on LAS or DBSA have

serious biodegradation problems mainly owing to the benzene group contained in LAS and

DBSA, which could lead to the environmental pollution. In this study, two kinds of benzene-

free metal sulfonate surfactants such as neutralized calcium sulfonate (NCS) and OCS

(overbased calcium sulfonate) were synthesized to replace LAS or DBSA for lubricant

formulations and the structure of the synthesized products were elucidated by 1H NMR,

13C-

NMR and FT-IR. The term overbased indicates that the quantity of colloidal calcium

carbonate in the particle cores is greater than that is needed to neutralize the acidic surfactant,

otherwise it is described as neutral, indicating that the overbased detergents have a greater

acid neutralizing capacity than their neutral salts. The biodegradability and long-term stability

of the resulting products were characterized and the interfacial properties were also measured.

The performances of prepared lubricants prepared with NCS and OCS respectively were

measured such as oil stain protection, rust inhibition and lubrication and compared with that

of lubricant based on LAS.

EXPERIMENTAL

Lauryl alcohol with a purity of greater than 98% and sulfuric acid with a purity of greater than

99% were purchased from Samchun Pure Chemical Co. and were used without any further

purification. NaCl, KOH, anhydrous sodium sulfate, chloroform and ethyl alcohol were also

received from Samchun Pure Chemical Co. and were used as received. Calcium carbonate

(CaCO3) nanoparticles with a purity of greater than 98.3%, the whiteness of 97.0 L and the

average particle size of 78.4 nm were supplied by Dongyang M&M Industry Co., Korea.

Hydrochloric acid solution (1.0 M HCl) and sodium hydroxide solution (0.1 M NaOH) with a

purity of greater than 98% were purchased from Sigma-Aldrich Co. and n-decane of purity

greater than 99% was obtained from Sigma-Aldrich. Water used for sample preparation was

ultrapure, which have been double distilled and passed through a Nanopure (Sybron-

Brinkman Inc.) ion exchange system.

In this study, NCS and OCS were synthesized through the following steps (Schemes 1 and 2).

The benzene-free sulfonic acid intermediate was prepared via the sulfonation of 1 mole of

lauryl alcohol by sulfuric acid and then followed the neutralization of sulfonic acid

intermediate using 1 mole of Ca(OH)2 for 3 hrs. The yield and TBN of NCS were found to be

98% and 99 mg KOH/g respectively. For the preparation of OCS, the sulfonic acid

intermediate was prepared via the sulfonation of 1 mole of lauryl alcohol by sulfuric acid and

then followed the neutralization of sulfonic acid intermediate using 4 moles of Ca(OH)2. A

small amount of acetic acid was added as a polar promoter to the reaction mixture prior to

bubbling carbon dioxide into the reaction vessel. Finally, the overbased products went

through the carbonation using CO2 gas to produce OCS. The yield and TBN of OCS were

found to be 97% and 310 mg KOH/g respectively.


Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26

2 C12H

Scheme 1 Synthesis route of

2 C12H25SO3H Ca(OH)2 CO2 gas

Scheme 2 Synthesis route of overbased

The structure of intermediates and final products were elucidated by

FT-IR spectrophotometer. 1H-

400 and expressed as δ units at room temperature in CD

spectrometer was used to obtain IR spectra of

molecular structure, molecular weight,

properties of LAS were also included in Table 1 for comparison.

Table 1 -

Molecular Structure

LAS

NCS

OCS NCS + amorphous

During this study, the CMC of surfactants was determined by measuring the surface tension

of a surfactant using a Du Noüy

CMC was considered to reach when there was no further decrease in surface te

increase in surfactant concentration

bubble pressure tensiometer (Kruss BP2, Germany), where the range of bubble life time used

was from 10 to 60,000 ms. The interfacial tension between 1 wt%

decane oil was measured at 25

equipped with a video camera (Sony SSC

DSA100, Germany) has been used to measure a contact ang

surfactant solution on a glass micro slide. The DV

measure the viscosity of a surfactant solution. The stability of aqueous surfactant solutions

was evaluated by using an emulsion stabil

conductivities of top and bottom portions of a sample bottle of a surfactant solution were

measured at 25℃ and the difference between two conductivity values was used to estimate

stability of surfactant solutions.

The biodegradability test of NCS and OCS was conducted according to the OECD 301 E test

for ready biodegradability. The performances

oil stain protection and rust inhibition (salt spray, wetting)

formulated using 90% of naphthenic base oil, 3% of surfactant and 7% of



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C12H25OH + H2SO4/SO3 → C12H25SO3H

H25SO3H + Ca(OH)2 → (C12H25SO3)2Ca + 2 H2O

Synthesis route of neutralized calcium sulfonate (NCS)

Ca(OH)2 CO2 gas [C12H25SO3

-]2 Ca2

+ + amorphous CaCO

Synthesis route of overbased calcium sulfonate (OCS)

The structure of intermediates and final products were elucidated by 1H-NMR,

-NMR and 13

C-NMR spectra were recorded on a Br

units at room temperature in CD3OD. Digilab's FT-

spectrometer was used to obtain IR spectra of NCS and OCS surfactants.

molecular structure, molecular weight, pH and viscosity of NCS and OCS

AS were also included in Table 1 for comparison.

Summary of the properties of LAS, NCS and OCS

Molecular Structure MW (g/mol) pH

326.49 1.001

875.25 12.313

amorphous CaCO3 875.25 12.090

of surfactants was determined by measuring the surface tension

Noüy ring tensiometer (Sigma702, Biolin Scientific) at 25°C

CMC was considered to reach when there was no further decrease in surface te

increase in surfactant concentration. Dynamic surface tension was measured by a maximum


was from 10 to 60,000 ms. The interfacial tension between 1 wt% surfactant solution and n

decane oil was measured at 25°C using a spinning drop tensiometer (SITE 100HS, Kruss

equipped with a video camera (Sony SSC-DC374, Japan). Drop shape analysis system (Kruss

DSA100, Germany) has been used to measure a contact angle at 25℃ by forming a drop of

surfactant solution on a glass micro slide. The DV-II+ digital viscometer was utilized to


was evaluated by using an emulsion stability tester (DualCon ITEC, Germany). The electrical


and the difference between two conductivity values was used to estimate

lutions.


The performances of prepared lubricants were measured such as

oil stain protection and rust inhibition (salt spray, wetting), where

aphthenic base oil, 3% of surfactant and 7% of paraffin mineral oil

SO

O O-2

Ca2+

+ amorphous CaCO3

NMR, 13

C-NMR and

NMR spectra were recorded on a Bruker DPX

-IR FTS-165 FT-IR

surfactants. Table 1 shows

OCS surfactants. The

Viscosity

(cP)

20.6

12.313 11.0

12.090 5.0

of surfactants was determined by measuring the surface tension

ring tensiometer (Sigma702, Biolin Scientific) at 25°C. The

CMC was considered to reach when there was no further decrease in surface tension with an

Dynamic surface tension was measured by a maximum


surfactant solution and n-

SITE 100HS, Kruss)

DC374, Japan). Drop shape analysis system (Kruss

by forming a drop of

II+ digital viscometer was utilized to


ity tester (DualCon ITEC, Germany). The electrical


and the difference between two conductivity values was used to estimate


s were measured such as

the lubricant was

paraffin mineral oil

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on a weight basis. The tribological properties were evaluated on a four-ball machine. The

antiwear and friction-reducing properties were determined under the following conditions:

speed 1200 rpm, load 500 N and room temperature. The surface of a lubricated specimen

made of stainless steel (5cmx5cm) was observed by an optical microscope (Nikon LV100

Pol).

RESULTS AND DISCUSSION

Two kinds of benzene-free metal sulfonate surfactants such as neutralized calcium sulfonate

(NCS) and OCS (overbaesd calcium sulfonate) were synthesized to replace LAS or DBSA in

lubricant formulation. The structure of NCS and OCS was characterized by 1H-NMR,

13C-

NMR and FT-IR and the results are shown in Figs. 1 and 2.

In this study, the CMC was determined by measuring the surface tension of a surfactant as a

function of concentration. The CMC was taken as the concentration beyond which the surface

tension of the aqueous solution does not decrease any more. In addition to CMC, other

interfacial properties such as surface tension, interfacial tension, contact angle and foam

stability were measured at 25℃ and the results are summarized in Table 2.

Table 2 - Summary of interfacial properties of LAS, NCS and OCS

CMC (mol/L) Surface Tension (mN/m)

Interfacial Tension

(mN/m) Contact Angle (°)

LAS 5.00e-4

34.15 0.034 14.89

NCS 6.69e-3

31.65 0.022 11.37

OCS 9.82e-3

22.37 0.162 40.88

As shown in Table 2, the CMCs of LAS, NCS and OCS surfactant systems in mol/L are

5.00x10-4

, 6.69x10-3

and 9.82x10-3

respectively. The CMCs of NCS and OCS surfactant

systems are found to be larger than that of LAS mainly due to the large molecular weight of

NCS and OCS. Surface tensions of aqueous surfactant solution at CMC condition are

summarized in Table 2. As shown in Table 2, the surface tensions of LAS, NCS and OCS are

34.15, 31.65 and 22.37 mN/m respectively. It is noticeable that the surface tensions of NCS

and OCS are lower than that of LAS. As shown in Figs. 3, 4 and 5, dynamic surface tension

measurement using a maximum bubble pressure tensiometer indicated a sharp decrease in the

surface tension of the aqueous surfactant solution with an increase in concentration of the

surfactant solution. In addition, all of LAS, NCS and OCS surfactant systems required

relatively shorter time to reach an equilibrium value presumably due to the high mobility rate

of surfactant molecule. This result indicates that any depletion of surfactant molecules from

the air/water interface will be replenished by an instantaneous diffusion of molecules from the

bulk aqueous solution. Interfacial tensions were measured as a function of time for n-decane

drops brought into contact with 1 wt% surfactant solutions at 25℃. As Figs. 3, 4 and 5

indicates, the interfacial tension between an aqueous surfactant solution and n-decane dropped

over a period of about 20~30 min to an equilibrium value. The equilibrium values of LAS,

NCS and OCS surfactant systems are 0.034, 0.022 and 0.162 mN/m respectively. It is worthy

pointing out that the interfacial tensions measured between surfactant solution and n-decane

oil are in the same order of magnitude as those exhibited between micellar solutions and

nonpolar hydrocarbon oils. The contact angle measured for 1 wt% of LAS, NCS and OCS

surfactant systems were found to be 14.89°, 11.37° and 40.88° respectively.



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(a)

(b)

(c)

Fig. 1 - Spectral data of NCS; (a) 1H NMR spectrum, (b)

13C NMR spectrum, (c) FT-IR spectrum

SO

O O-2

Ca2+

SO

O O-2

Ca2+

a b c

SO

O O-2

Ca2+

a b c

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(a)

(b)

(c)

Fig. 2 - Spectral data of OCS; (a) 1H NMR spectrum (b)

13C NMR spectrum, (c) FT-IR spectrum



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Concentration (mol/L)

1e-5 1e-4 1e-3 1e-2 1e-1Surface Tension (mN/m)

20

40

60

80

(a)

Surface Age (ms)

1e+1 1e+2 1e+3 1e+4 1e+5

Surface Tension (mN/m)

0

20

40

60

80

5.0 E-6 (mol/L)

5.0 E-5 (mol/L)

1.0 E-4 (mol/L)

5.0 E-4 (mol/L)

1.0 E-3 (mol/L)

5.0 E-3 (mol/L)

(b)

Time (min)

0 10 20 30 40 50

Interface Tension (mN/m)

0.02

0.04

0.06

0.08

0.10

(c)

Fig. 3 - Interfacial property measurement for LAS surfactant; (a) static surface tension, (b) dynamic surface

tension, (c) interfacial tension

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1e-5 1e-4 1e-3 1e-2 1e-1

Surface Tension (mN/m)

20

40

60

80

(a)

Surface Age (ms)

1e+1 1e+2 1e+3 1e+4 1e+5Surface Tension (mN/m)

0

20

40

60

80

6.69 E-5 (mol/L)

1.34 E-4 (mol/L)

6.69 E-4 (mol/L)

1.34 E-3 (mol/L)

6.69 E-3 (mol/L)

1.34 E-2 (mol/L)

6.69 E-2 (mol/L)

(b)

Time (min)

0 20 40 60 80 100Interface Tension (mN/m)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

(c)

Fig. 4 - Interfacial property measurement for NCS surfactant; (a) static surface tension, (b) dynamic surface




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0.001 0.010Surface Tension (mN/m)

20

40

60

80

(a)

Surface Age (ms)

1e+1 1e+2 1e+3 1e+4 1e+5Surface Tension (mN/m)

-20

0

20

40

60

80

1.09 E-3 (mol/L)

3.27 E-3 (mol/L)

6.55 E-3 (mol/L)

9.82 E-3 (mol/L)

1.31 E-2 (mol/L)

1.64 E-2 (mol/L)

(b)

Time (min)

0 10 20 30 40 50

Interface Tension (mN/m)

0.16

0.18

0.20

0.22

(c)

Fig. 5 - Interfacial property measurement for OCS surfactant; (a) static surface tension, (b) dynamic surface


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The biodegradability of NCS and OCS surfactants was found to be 86% and 93%

respectively, indicating excellent biodegradation. In order to measure the performance of

lubricant based on NCS and OCS, oil stain protection, anticorrosion and lubrication properties

were evaluated. The performance of lubricant prepared with LAS surfactant was also

measured for comparison. The lubricant was made of 90% of naphthenic base oil, 3% of

surfactant and 7% of paraffin mineral oil on a weight basis. The results of lubricant

performances are shown in Figs. 6, 7 and 8. The result was also summarized in Table 3 for

performance comparison of each surfactant. The performance of oil stain protection was

measured for lubricants prepared with LAS, NCS and OCS respectively by observing the

surface of a lubricated specimen made of stainless steel by using an image analyzer. As

exhibited in Fig. 6, no oil stain was observed in all of three surfactant systems, suggesting that

oil stain protection capacity of NCS and OCS is comparable to that of LAS. The result of rust

inhibition test by a salt spray method was shown in Fig. 7. No corrosion was observed with

OCS while the extents of corrosion for LAS and NCS were observed to be 4% and 2 %

respectively. On the other hand, the rust inhibition test by a wetting method revealed no

corrosion in all of three surfactant systems. The tribological property was evaluated on a four-

ball machine under the following conditions: speed 1200 rpm, load 500 N and room

temperature. As summarized in Table 3, the load-wear index (LWI) values measured for the

lubricant detergents prepared with LAS, NCS and OCS were found to be 21%, 28% and 31%

respectively. This result implies superior lubrication efficiency of the products based on NCS

and OCS.

Table 3 - Summary of the performance of lubricant additives prepared with NCS and OCS

Test Items Unit LAS (Reference) NCS OCS Methods

Oil Stain (24 hrs) - Not occur Not occur Not occur MIL-C-22235A

Rust Inhibit

(24 hrs)

Salt spray % 4 2 No corrosion KSM 2109

Wetting - No corrosion No corrosion No corrosion KSM 2109

Lubricating (Four-ball) *LWI 21 28 26 KSM 2026

CONCLUSIONS

In this study, environmental friendly benzene-free metal sulfonate surfactants were

synthesized for lubricant formulation and the structure of intermediates and final products

were elucidated by 1H NMR,

13C-NMR and FT-IR. Also, the interfacial properties such as

critical micelle concentration, surface tension, contact angle, interfacial tension, foam stability

and emulsion stability were measured. The biodegradability and long-term stability of the

resulting products were characterized and the performances of prepared lubricants using

synthesized surfactants were measured such as oil stain protection, rust inhibition and

lubrication. The performances test of prepared lubricants have shown that both lubricant

formulations prepared with NCS and OCS exhibited excellent performances such as oil stain

protection and rust inhibition compared with that prepared with LAS. This result indicates



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that the newly synthesized surfactants, such as NCS and OCS, are potential candidates to

replace LAS and DBSA in lubricant formulation.

(a) (b) (c)

Fig. 6 - Oil stain test result; (a) LAS, (b) NCS, (c) OCS

(a) (b) (c)

Fig. 7 - Rust inhibition test result by a salt spray method; (a) LAS, (b) NCS, (c) OCS

(a) (b) (c)

Fig. 8 - Rust inhibition test result by a wetting method; (a) LAS, (b) NCS, (c) OCS

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PREPARATION OF ENVIRONMENTAL FRIENDLY · PDF filedispersing, emulsifying, stabilizing, foaming, conditioning and anti-foaming agents in many ... detergents, soaps, ... acid neutralizing